This is how celebrity works. One duck-egg-blue day in Los Angeles, you find yourself speed-walking down a terracotta path at the Hotel Bel-Air. Hustling beside you is the global PR of Walt Disney Studios, a natty Brit. You thought your interview was in an hour, but no, says the natty Brit, it's now, and no, you don't have 30 minutes, you have 25, and no, there's no time to go to the toilet. This is what happens when you've been flown halfway around the world to meet perhaps the most famous movie star alive, and perhaps the most beautiful woman on the planet. The rules of normal life no longer apply.

I think very much children are exactly who they are when they're born.

The natty Brit swings left into a corridor, and takes a flight of stairs two at a time. At the top, another PR stands in the gloom, guarding a door. It opens and ejects a journalist. Propelled from behind, you plunge forward and into the light.

If this story were a movie, such light would signify a revelation. But in fact, Angelina Jolie is side-on, pouring a glass of water at a cabinet to your left, so your first, anticlimactic vision of her is of a slim figure in profile, head bent, one knee cocked. She is wearing all black: skinny black jeans and a loose black top. She turns, smiles, steps around a coffee table to a sofa on your right. You shake hands. You think she seems strong: a strong grip. Tattoos on her inner arms. Broad shoulders. Slim - but not skeletally slim. All this hits you in a second. So it is not until your second second that you register Angelina Jolie's face.

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Great beauty is hard to describe. Even Homer only managed "white-armed Helen"; so much is subject to collective opinion and individual mood. But Jolie, in the flesh, is a kind of fact. Every now and then - once in a generation? Once in a century? Once in an age of heroes? - a face appears that makes the launching of a thousand ships seem reasonable. Jolie has that face.

Clint Eastwood - not easily impressed - once called Jolie "the most beautiful woman on earth", and this may, quite literally, be true. You might say, "No, a more beautiful woman may be living in darkest obscurity somewhere," but in fact you realise, as soon as you meet the 38-year-old Jolie, that beauty like this is absolutely incompatible with anonymity. As soon as a single other Homo sapiens caught sight of it, the gig would be up.

Maleficent: Angelina Jolie with her daughter Vivienne Jolie-Pitt, who was the only young Aurora not to cry at the sight of Jolie.

Jolie's colouring is all in shades of brown: honey- brown hair, pale-gold skin, amber-green eyes. Even her lips - as extraordinary in life as on film - are caramel pink. She has not a single line, mark or blemish on her face, but manages to look as if she hasn't had Botox or work done of any kind. (She may have, of course, which means she's found the best cosmetic surgeon in world history, which in turn raises the question of why more stars haven't done the same, which in turn suggests she hasn't.) She does seem to be wearing false eyelashes, but they're like no false eyelashes you've ever seen: they seem to have been applied one by one, possibly under a microscope by a highly skilled eyelash genie.

She also has an unexpectedly lovely voice, low-pitched and clear. Obedient to the PRs listening at the door, and the loudly ticking 25-minute stopwatch in your head, you ask about her latest movie.

It is her 38th, in a career spanning everything from mental patient in Girl, Interrupted (for which she won an Oscar in 2000) to pneumatic cartoon heroine Lara Croft. It is a Disney production, entitled Maleficent, and revolves around the wicked fairy/queen/witch (Disney doesn't get bogged down in details) who curses Sleeping Beauty. Jolie plays Maleficent, notable for her unearthly green beauty, a faint sibilance in her voice, and her prosthetic cheekbones, even higher and more angular than Jolie's own.

Complicated history: With her brother, James Haven, and father, Jon Voight, in 1994. Photo: Getty Images

What is most notable about this film, however, at least in celebrity terms, is that Angelina is not the only Jolie in it. Her 10-year-old son, Pax Jolie-Pitt, and her nine-year-old daughter, Zahara, have brief walk-on parts, and the blonde, dazzlingly cherubic child who plays the young Sleeping Beauty (aka Aurora), is Jolie's youngest daughter, five-year-old Vivienne. How did this happen?

"Well, Aurora needs to be a kid who can really, genuinely see me with love, and not be afraid," explains Jolie pleasantly. "And I'm there with my horns and my accent and my pointy teeth, saying things like, 'I hate you! Go away!' "

Children did, apparently, run screaming from the set at the sight of Jolie in costume. "Two little children broke down in tears, and one said, 'Mummy, please make the scary lady stop talking to me.' " Vivienne, however, took it in stride. "She's the mummy's girl: she's the one who's constantly attached to my kaftan at home." Jolie smiles. "Actually, she's very good in her scene. It made us slightly uncomfortable."

Creeping beauty: Angelina Jolie as Maleficent.

The "us" here is, of course, Brad Pitt: mega movie star in his own right, Jolie's partner of a decade, and the father (adoptive and biological) of her six children. You know this, of course, but even this small mention is surprising. Most celebrity interviews are understood by both parties as a kind of duel to the death: you with your cunningly disguised "tell me about your personal life" sword thrusts, they with their elaborate "let me describe yet another intensely boring detail about my work" defensive ripostes. Yet here is Jolie, rolling happily on with what interests her, which also happens to be what interests everybody else, which is real life (strange as it may seem to apply the concept to a plane-piloting, UN-ambassadoring, nation-hopping, film- star-partnering superwoman).

"We're hoping, I think, that the kids don't become actors," she confides. "We want them to be happy, and do whatever they're interested in, but I think we're hoping to show them so many other ideas and other options that they won't want to act. If they do, I hope they act and also ..." she pauses, perhaps trying to be diplomatic, "... do something else. I'd like them to do other things with their lives." She shakes her head. "We're a bit nervous about that."

You try, and fail, to imagine Jolie and Pitt worrying about their kids like normal people. You also try, and fail, to care about asking more movie questions. Instead, you ask her if she and Pitt have an acting-prevention plan. Jolie puts her elbows on her knees, looking exactly like a mother gossiping beside the school gate - except, of course, that she looks absolutely unlike any other imaginable mother on earth.

Ambassador: In Kenya in 2009 as a Special Envoy to the UN High Commissioner for Refugees. Photo: AustralScope

"Well, we think it's almost good that they come to set," she says, "and we let them come to a premiere here and there. We don't want to keep them from it: we want them to see it so they can get bored by it." She looks triumphant. "And our eldest does seem quite bored about it all; he finds it a little fun, but he's very into music and he's not that taken by film."

You can't help thinking that this might mean she and Pitt will be dealing with a wannabe rock star in 10 years' time, not a third-generation actor (Jolie's father, Jon Voight, is also an Oscar-winning actor; his most famous role was in the 1969 hit Midnight Cowboy), which might not be a notably easier path. How much influence does she think parents really have over their kids?

"I think very much children are exactly who they are when they're born," she says. "And if there's a trauma, it can drastically change who they are, but if there isn't, they will most likely be ... We look at our kids, and if you look at baby photos of them, the way they were, the way they looked, what their kind of energy was - whether they were a sweet, elegant, private little person, or a funny, open person, or a bold person, or whatever - they're still exactly the same. There's so much that they're born with. And we believe that you have to just encourage the individual and support them, but don't get in their way too much.

"And what's fascinating," she goes on, "is that you could say, 'Well, you'd be more similar to the children who have a genetic link to you,' but I'm not. Maybe one of them, but then I'm also very similar to [her adopted son] Maddox. So it doesn't have an impact that some are genetically connected."

Speaking of genetics, several years ago Jolie explained that she couldn't imagine having biological children. Now she has three. With 15 of your 25 minutes down, you throw caution to the wind. What changed her mind? "It took me a really long time," she says easily. "It was very important to me that I came together with a man to whom it didn't matter whether we ever had children, and who was completely content to only adopt. And when I saw Brad with our children and I saw that they really were his children, and there was nothing missing for him, then it became clear to me that this was a journey we should go on together, and that it was another way of being parents.

"It was an additional way, not changing the course of our family - we would still adopt, and we did. But it was very important that it wasn't because he felt like something was missing with an adopted child. I waited for that moment to make sure he didn't see it that way."

Jolie herself knows about things missing in childhood: Jon Voight left her mother, Marcheline Bertrand, when Jolie was two. Bertrand raised Jolie and her older brother, James Haven, as a single mother, and Voight has been an unreliable, sometimes overtly hostile figure in his daughter's life, criticising her in the press, once even suggesting she was mentally unstable. Yet last year, when she received the Jean Hersholt Humanitarian Award (an honorary Oscar awarded to a member of the film industry for humanitarian work), he was in the audience, on the same table as Brad and Maddox. How is their relationship these days?

"We have a very complicated history," says Jolie, speaking slowly. "And we got to a place where we made an agreement, so my children would know him, that we would just never speak about the past. So we don't really, we just, we don't ..." She pauses. "One of the things you tend to do, especially in families where you fight often, or have a deep history or a lot of pain, there's this constant desire for people to try to correct it, or reinvent it, explain it.

"With us, we just got to a point where there was no going back, and there was going to be no ... We were never going to come to terms with certain things, and my mother's no longer alive to defend herself. So we kind of know each other today, as we are today. And we don't discuss the past, and it's not really a father-daughter relationship, as much as we try to be friends to each other at this time." She pauses again. "It became very simple, that I didn't feel it was right for my kids not to know him, and him not to know them. But you know, it has to be kept simple. So we don't go backwards."

Jolie's mother Marcheline, whom she clearly adored, died in 2007, at only 56, after an eight-year battle with ovarian cancer. During her speech last year in accepting the Jean Hersholt Oscar, Jolie made an unusual reference to Marcheline in the context of the slick, everyone's-a-winner awards ceremony. "My mother loved film," she said. "But she never had a career as an artist; she never had the opportunity to express herself beyond her theatre class."

Her eldest son Maddox, now 12, was in the audience, and Jolie went on to address him directly, telling him how happy she was to be his mother; how wonderful and privileged and fortunate her life was. The happiness of parents, she seemed to be saying, really matters to children.

"Yes," she says, leaning forward. "Yes, that's very true. Exactly. My mom was the greatest mother, and she couldn't do anything about the fact that we were often in a situation where I was worried about her, or wanting to take care of her. And I do hope my children never have to do that. But already they see that their father takes care of their mother, and that's something that I didn't see. So that's an extraordinary thing. And I think about it often - I'm very conscious of telling my kids how happy I am in my life. Even if I seem tired, or whatever: that I'm happy to do homework!"

She gives a slightly goofy laugh. "I want them to know that their lives take priority, and their concerns are more important than any of my concerns. Their needs are more important than my needs and my turn is passing and their turn is next. And I'm happy to do that."

As a mother, Jolie asks her children to travel constantly in pursuit of her and Pitt's film work, and exposes them to the disturbing, albeit absolutely real, problems of refugees and people in conflict all over the world through her role as a special envoy to António Guterres, the UN High Commissioner for Refugees. But by her reasoning, this is far better than asking them to carry the anxiety of knowing she's unhappy, and feeling, as children, that they need to fix it. This is what happened to her, she says: she became an actress because her mother wanted her to.

"Well, you want to be what they think would be the best thing for you," she says, smiling. "And she really wanted to be an actress, then she wanted it for me. But it took me only until a few years ago to realise that I don't know if I ever really wanted it. And that's a weird thing to realise: you wanted to fulfil a dream - and I've had a great life and learnt so much - but maybe it wasn't my dream. It was very interesting to me to try to do something else creatively and realise how much more it fit me than the thing I'd been doing all my life."

It's hard to imagine Angelina Jolie ever having done anything she didn't want to do. The very laws of the universe, you can't help thinking, would rise up and prevent it. But then, the universe is a fickle mistress. Last year, Jolie underwent a preventative double mastectomy, having discovered she carried a BRCA1 gene mutation that, without surgery, gave her an 87 per cent chance of contracting breast cancer.

It's likely she will have more preventative surgery in the future, most probably an oophorectomy (removal of her ovaries) to eliminate the chance of ovarian cancer (the other cancer for which her mutation puts her at high risk). More immediately, she'll finish the film she directed recently in Australia, Unbroken, and co-chair the Global Summit to End Sexual Violence in Conflict. She might also get married - belatedly, you realise she's wearing the extremely enormous, extremely beautiful white-and-yellow diamond ring that Pitt designed for her in 2012 when the pair announced their engagement - or adopt another baby.

It feels, sitting there opposite her, that you could ask about any or all of these things, and Jolie would answer. But then the door swings open, and the natty Brit is standing there, looking meaningful. Your time - all 23 minutes of it - is up. You stand up, say goodbye. She smiles. And out you go, back into the dim corridor. Oddly, it now doesn't seem so dim, nor the room so bright. It's just that both fame and beauty polish a person so they catch the light, and in Jolie's case the dazzle is almost blinding. But the person is there all the time. Which is a nice surprise about the way celebrity works.